I came across a problem today with Mozilla Thunderbird (though not necessarily isolated to this client) and the POP mail server. It came about because a user has been out of the office and not pop’ing his mail to the desktop. The server had accumulated 100MB of email over this time.
Thunderbird has a default pop timeout of 45 seconds. In that 45s, the client must authenticate, the server must create a lock file, and copy over the mail spool into a temporary file, before Thunderbird can begin downloading the mail. If the server cannot copy the 100MB mail file into a temporary file within the 45second limit the timeout message occurs.
to the end will increase the timeout to 300 seconds. After relaunching, Thunderbird can successfully download mail without the poplock busy error.